Sterilization consists in destroying a significant number, in a given proportion, of microorganisms, viruses, or pathogenic proteins present on the inside or outside surfaces of articles to be sterilized.
It should be observed that the adjective “sterile” is an absolute term, whereas ensuring that an article is sterile, i.e. free from microorganisms, is a probability function. The sterility assurance level (SAL) of an article is defined as the probability that any given unit is not sterile after being exposed to a validated sterilization process. Thus, for an article to be considered as being sterile with respect to European standard EN556, it must possess an SAL of 10−6, i.e. the theoretical probability of isolating a microorganism must be less than 1 in 106.
Various sterilization processes are known, including chemical and physical processes.
Amongst chemical sterilization processes, there sterilization processes use gases such as ethylene oxide, formaldehyde, or hydrogen peroxide. Those processes nevertheless present the drawback of requiring a long period of time for desorption, and that is incompatible with the instruments for sterilizing being made rapidly available. In addition, those gases are toxic and irritate the skin and the mucous membranes.
Physical processes include in particular steam sterilization in an autoclave under the action of temperature and steam; dry hot sterilization; radiation using ion beams or gamma rays, used on articles that cannot be sterilized by means of heat or chemically; or indeed filtering using filters that are suitable for separating out microorganisms. Those processes generally involve high temperatures, often higher than 100° C.
Because of the increasing use in medical articles of materials that are temperature-sensitive, such as polymer-based materials, it is desirable to develop sterilization processes usable at low temperature, and in particular at temperatures lower than 70° C.
Sterilization processes have thus been developed that makes use of a plasma, operating at temperatures that makes it possible to avoid damaging temperature-sensitive materials.
For example, application WO 00/72889 discloses a sterilization process that uses a plasma based on oxygen and nitrogen. Application FR 2 856 600 describes a sterilization process making use of a post-discharge plasma coming from a plasma made exclusively of nitrogen, while application FR 2 879 933 uses a post-discharge plasma coming from a plasma made up of hydrogen and of nitrogen. Numerous sterilization processes thus make use of a gas based on nitrogen or oxygen for preparing the plasma.
In order to validate sterilizers, use is made of sterilization indicators that make it possible to monitor one or more essential parameters of the sterilization process. For this purpose, three types of sterilization indicator have been developed: physical, chemical, and biological indicators.
Sterilization indicators for processes making use of a plasma are still little developed. Documents U.S. Pat. No. 6,659,036, WO 98/46279, JP 2005111154, and JP 2004298479 disclose sterilization indicators relating to processes that make use of plasma. Nevertheless, those documents do not relate to plasmas based on nitrogen and/or oxygen.
It thus appears necessary to have sterilization indicators available that enable at least one parameter of the sterilization process to be evaluated for sterilization processes making use of a post-discharge plasma obtained from a gas comprising nitrogen N2 and/or oxygen O2.